Over the years various means have been devised to collect solar energy and to convert the same into thermal energy. One of the more typical forms of solar collectors is generally termed the flat plate collector and usually consists of a metal absorber plate painted black on the side facing the sun and thermally insulated on the sides and back thereof. Planely spaced above the absorber plate are usually one or more transparent glass or plastic covers to reduce heat loss in that direction. The thermal energy absorbed by the absorber plate or material is usually transferred to a working fluid (either liquid or gaseous) by circulating the same through tube like conduits that are either in thermal contact with or in close proximity to the absorber plate or material. The choice of materials for the absorber plate and working fluid tubes have up to now been dictated by the necessity for both a good thermal conductor and a material which is durable under normal exposure conditions of solar collecting. Usually either copper, aluminum or a combination of the two are used. The reason for these choices is, of course, that the metals are good thermal conductors and have reasonable durability.
Because of the relatively large expense associated with the metal tubing such as copper or aluminum, coupled with their relatively high thermal conductivity values (0.918 cal/cm/ sec/c and 0.480 cal/cm/sec/c, respectively) adequately efficient, although far from highly efficient, collectors have been built using relatively wide spacing between tubing channels.
The disadvantages of using metals or metal components in solar collectors is first the high cost of processing and fabricating metal, coupled with eventual oxidation, corrosion and some cases deterioration through electrolysis or galvanic action. Additionally, the cost consideration restricts the design of highly efficient collectors and the general nature of metals restrict the various forms which can be employed in the design of such collectors.